The 3-D imaging technology disclosed in Stettner et al, U.S. Pat. Nos. 5,446,529, 6,133,989 and 6,414,746 provides with a single pulse of light, typically pulsed laser light, all the information of a conventional 2-D picture along with the third dimensional coordinates; it furnishes the 3-D coordinates of everything in its field of view. This use is typically referred to as flash 3-D imaging in analogy with ordinary digital 2-D cameras using flash attachments for a self contained source of light. As with ordinary 2-D digital cameras, the reflected light is focused by a lens on the focal plane of the LADAR sensor, which contains an array of pixels called a focal plane array (FPA). In the case of the terrain mapping LADAR sensor these pixels are “smart” and can collect data from which the time of flight of the laser pulse to the object of interest can be calculated. Each smart pixel also collects data associated with the returning laser pulse shape and magnitude.
One value of these flash LADAR sensors, as opposed to competing designs in which one or more pixels is scanned over the field of view, is the elimination of the precision mechanical scanner, which is costly, high maintenance and typically large and heavy. The pixels in the focal plane of a flash LADAR sensor are automatically registered due to their permanent positions within the array. Further, by capturing a frame of data as opposed to one or a few pixels with one laser pulse, the data rate is greatly increased while weight and volume are reduced. Because each frame of data is captured from the reflection of a short duration laser pulse, moving objects or surfaces of stationary objects may be captured from a moving platform without blurring or distortion. The instant invention is a flash LADAR sensor specifically adapted to a low cost, lightweight, unmanned aerial vehicle (UAV) further adapted for terrain mapping applications.
The first embodiment of the terrain mapping flash ladar sensor includes stationary optics and a focal plane array of two rows of N pixels each (2×N array), where N=128 for example. If the ladar sensor platform is in motion and the ladar sensor covers the entire field of view (FOV) normal to the platform motion on the ground, then a continuous 3-D map can be generated by pulsing the laser fast enough so frames are overlapped without the necessity of any moving mechanical parts. At higher speeds or higher elevations, a mechanical pivot advances the angle of the illuminating laser pulse so it will be received on the return path by one of the rows of the focal plane array. Alternatively, for high speed platform motion or high altitude, the mechanical pivot may be eliminated and the focal plane array may be moved linearly rearward by a linear motion translation stage, so the illuminating laser pulse may be received by one of the rows of the focal plane array. For larger fields of view, or higher motion velocity, larger M×N or N×N focal plane arrays can be generated by making arrays with a greater number of rows and columns, or by using multiple smaller focal plane arrays.
In all the terrain mapping flash LADAR sensor embodiments, flash ladar data is developed into a 3-D map using software which stitches the frames together. By using a proper water-penetrating laser wavelength and a particular “range gated” data collection mode in the terrain mapping flash ladar, underwater objects and sea floors and lake bottoms can be mapped. The same mode of operation will allow mapping through smoke and fog or mapping of smoke, fog, or gas clouds.